It became the leading topic of discussion during Saturday’s Democratic presidential debate: What should the United States do in the fight against ISIS following the attack on Paris?

In the days since the massacre overseas, the presidential hopefuls have offered an array of opinions, with several of the Republicans contenders coming out in favor of doing more; even if that means American “boots on the ground.”

One of the Paris attackers reportedly crossed into Europe alongside Syrian refugees, providing fuel to the argument, made by some GOP candidates, that ISIS could infiltrate the 10,000 Syrian refugees President Obama vowed to accept over the next year.